As disclosed in Japanese Patent Application Laid-Open (kokai) No. 2008-70194, there has been known a technique of electrically cutting off (breaking) the continuity between a gas sensor and a sensor control apparatus, thereby preventing flow of current into the gas sensor, when a wiring anomaly occurs and some of wiring lines electrically connected to the gas sensor are shorted to a power supply potential or a ground potential. The technique can reduce the possibility of an excessive current flowing into the gas sensor and breaking the gas sensor.